The present invention relates to an improved disposable tip member for single and multiple channel pipette devices.
The use of pipette devices for the transfer and dispensing of precise quantities of fluids in analytical systems is well known as is the use of disposable tip members for such pipettes. Disposable tips accommodate the serial use of such pipette devices in the transfer of different fluids without carryover or contamination.
Generally speaking, disposable tip members are formed of a plastic and are of an elongated conical shape with an open proximal end for receiving and releasably mating with the distal end of the pipette's conical tip mounting shaft. Ideally, the disposable tip member should slide easily onto the pipette shaft to an axial position adjacent the pipette's tip ejection mechanism. Thus located, the tip member should be stable on the shaft, free from external rocking relative to the shaft (as during "tipping off"), and form a fluid tight annular seal with the pipette shaft.
Unfortunately, in practice, the ideal is rarely achieved without the exercise of special care and effort by the pipette operator in mounting the tip member on the pipette shaft. Commonly, disposable pipette tip members have a tendency to become loose with use, either destroying the necessary fluid seal with the shaft upon which it is mounted or falling off when subjected to side load forces as during "tipping off". To counteract such tendencies, pipette operators commonly force the tip member so far onto the pipette shaft that it becomes nearly impossible to remove or jams into the tip eject mechanism. At the very least, the variability of the insertion forces applied by a pipette operator in mounting flexible tip members on a pipette shaft usually results in the tip members being mounted in different axial positions during successive fluid transfer operations producing small quantitative variations in the fluids dispensed by the pipette.
The foregoing problems associated with the proper mounting of disposable pipette tip members are compounded with multichannel pipettes including several parallel shafts. Disposable pipette tips are commonly stored in sterilizable plastic boxes or racks where they are vertically oriented with their open proximal ends exposed. The multichannel pipette is placed over the rack with the several shafts thereof aligned with the open tips. After a slight initial insertion into the aligned tip members, a relatively large downward force is exerted on the pipette to drive the pipette shafts into the tip members. As the pipette shafts engage the tip members, such large downward forces are exerted on the tip members and transferred to the top of the rack causing it to bow and the tip members supported thereon to move with the now curved top of the rack. Under such conditions, the outermost tip members fully receive the pipette shafts while the innermost tip members do not. Such tip members often are not adequately seated on their corresponding pipette shafts and require separate manual pushing onto the corresponding shafts to create the desired fluid tight seals. Otherwise, such tips often fall off the shafts with pipette movement or dislodge with "tipping off."
The aforementioned problems associated with disposable pipette tips are common in varying degrees to all prior tip designs. One such tip design includes a smooth conical inner surface adjacent the open proximal end thereof. The axial taper of the inner surface is greater than the axial taper of the pipette shaft such that upon insertion, an annular end portion of the shaft engages an annular inclined inner surface of the tip member near the open end. Because such tip members are rather rigid, relative movement between the shaft and tip member stops almost immediately upon shaft engagement with the tip member resulting in a rather unstable annular seal and a tip member that is subject to rocking and dislodgement in response to lateral forces. These problems are particularly apparent when such tip members, mounted on deformable racks, are applied to multichannel pipettes. In particular, when such rigid tip members, mounted in a multi-pipette rack, are engaged by the multiple parallel shafts of a multichannel pipette, the tip members will seat on their associated shafts, canted relative to the shaft if the tip members are out of axial alignment with their associated shaft. This is because the tip members are too rigid to compensate for non-parallelism of the tip members mounted on the rack. Further, as such tip members are engaged by the multiple shafts, the downward forces cause the rack top to bow, resulting in the aforementioned non-uniform axial seating of tip members on the shafts or the non-seating of tip members on the inner ones of the shafts of the multichannel pipette. The problems of axial canting, unstable and uneven axial seating and/or loose central seating of tip members is common relative to all rigid tip members applied to multichannel pipettes. This is to be distinguished from the problems associated with prior flexible tip members. While some such tip members may be sufficiently flexible to compensate for non-parallelism of rack supported tip members, they easily receive the multiple shafts and seat at different axial locations on their associated shafts. This is due to the bowing of the rack top in response to the downward shaft insertion forces applied to the tip members and results in the aforementioned undesirable quantitative variations in fluids dispensed by several channels of the multichannel pipette. Further, such flexible tip members are subject to the aforementioned undesirable jamming into the tip ejection mechanisms of the multichannel pipettes in response to excessive axial forces, as may be applied to the outermost rack supported tip members during an attempt to properly seat the innermost tip members on a multichannel pipette.
Other tip designs include a single internal sealing band or crush ring adjacent the open proximal end of the tip member. Such tip members provide little if any axial guiding for the associated pipette shaft during insertion and are subject to the aforementioned problems of lateral instability. This is particularly true for tip members incorporating a crush ring. Such rings are permanently deformed as the pipette shaft is inserted into the associated tip member and do not possess the resilience necessary to accomodate any lateral tip movement on the shaft in response to external lateral forces commonly applied to tip members during use.
Still other tip members incorporate multiple internal sealing bands or crush rings. In practice, the walls of such tip members are usually so rigid that the tip members are subject to the aforementioned problems particularly associated with the application of rigid tip members to multichannel pipettes.
Commercially available pipette tip members having one or more of the foregoing shortcomings and/or characteristics are the Types RC20 and RC200 manufactured by Rainin Instrument Co., Inc. of Woburn, MA; Types C20 and C200 manufactured by Gilson Medical of Villiers Le Bel, France; Types 26, 28, 35, 37 and 40 manufactured by Bio Rad Laboratories of Richmond, CA; R-1035 BR manufactured by West Coast Scientific, Inc. of Emeryville, CA; Titertek.RTM. tips, Finntip and Finntip 60 manufactured by Labsystems OY of Helsinki, Finland; Types 9025 and 9026 manufactured by Medical Laboratory Automation, Inc. of Mount Vernon, NY; the Oxford.RTM. Types 810 and 911 manufactured by Sherwood Medical of St Louis, MO; Type P1100 distributed by Denville Scientific Inc. of Denville, NJ; Reference Tip.RTM. manufactured by Bio-Plas of San Francisco, CA; and ProPet tips manufactured by Cetus of Emeryville, CA; Eppendorf Flextip manufactured by Brinkmann Instruments Co. of Westbury, NY. Still others are described or referenced in U.S. Pat. No. 4,072,330.